The present invention relates to a method and a system for controlling a hybrid vehicle drive.
Hybrid vehicle drives have been on the market for some years as a consumption-reducing and environmentally friendly alternative to the conventional internal-combustion engine. By established general definition, a hybrid vehicle drive contains at least two different energy converters and two different energy accumulators. With a few exceptions, in a practical implementation, the converters involve an internal-combustion engine and an electric motor, and the energy accumulators are a combustible fuel and a battery.
In contrast to conventional vehicles having an internal-combustion engine, a hybrid vehicle has the advantage that it can recapture the braking energy for the most part (with the exception of the loss of efficiency). The recaptured or recuperated braking energy is intermediately stored in the battery of the electric motor, with the electric motor functioning as a mechanical-electrical converter.
An intermediate storage of energy (thus, the recuperation) occurs during active braking and in a coasting phase or operation in which the internal-combustion engine is not actively driving the vehicle because the driver's foot has been removed from the accelerator. The vehicle is therefore in a passive state and is propelled only by its own inert mass, until the diverse tractive resistances gradually decelerate it to a stop. In hybrid vehicle drives, the feeding of gasoline and the ignition are switched off in the coasting phase and technical measures are taken in order to stop the engine brake of the internal-combustion engine in the coasting operation. Thereby, the kinetic energy is caused to be supplied as completely as possible to the electric motor configured as a mechanical-electrical converter.
In a load point raising operation, the internal-combustion engine supplies a portion of its torque to the output and the remaining portion as the generator torque for the electric motor in order to thereby generate electric energy for the heavy-duty battery where the energy is stored. A disadvantage of the known hybrid vehicle drives was found to be that, in certain operating conditions, the load raising operation results in excessive fuel consumption.
An object of the present invention is to provide an improved method and system for controlling a hybrid vehicle drive that results in more fuel-saving during the battery charging operation.
The method according to the invention for controlling a hybrid vehicle drive and the corresponding system as hereinafter described have the advantage that the charging operation can be designed to be more flexible, and consumption advantages can therefore be achieved.
The present invention is based on the control calculating a fuel consumption parameter for the actual charging current of the battery for each gear, for example, the fuel mass flow rate, for several different gear positions of the transmission. By way of these gear-dependent fuel consumption parameters, the optimized gear with optimized fuel consumption, indicated by the respective fuel consumption parameter, such as the minimal fuel mass flow rate, is selected and is set by the transmission. Thus, the gear position is varied as a function of the operating point of the electric motor.
In the parallel hybrid—transmission line concept, during a constant travel with a constant wheel torque, the internal torque between the internal-combustion engine and the electric moment may be variable. In order to obtain an optimal operating point of the internal-combustion engine for the demanded actual charging current of the heavy-duty battery, according to the invention, in addition to the load of the internal-combustion engine and of the electric motor, the rotational speed of the assemblies is also varied by way of the gear selection.
According to a preferred further development, the fuel consumption parameter is a fuel mass flow rate. In another one of the currently preferred further developments, the determination of the least one fuel consumption parameter takes place for all gear positions of the transmission at the detected charging power.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.